1. Field of the Invention
The present invention relates to a dual type positive temperature coefficient thermistor device, i.e. a positive temperature coefficient thermistor device having a pair of positive temperature coefficient thermistors housed in an insulated case. The invention particularly relates to an improved arrangement for supporting each of the thermistors in the insulated case.
2. Prior Art Statement
The above-described dual-type positive temperature coefficient thermistor device can be applied to the degaussing circuit of a color television, for example, if one of the thermistors is used as a heat emitter and the other thermistor is used as a heat receiver. Typical commercial devices of this type are disclosed in Japanese Patent Public Disclosures No. 60-25205 and No. 60-259076, for example, and have a sectional construction as illustrated in FIG. 5.
This will now be explained as an example of a conventional device according to the prior art. Where appropriate, reference may be made to FIG. 2, which is an exploded perspective view of an embodiment of the device according to the present invention, as this embodiment has the same structure as the prior art example, except for those parts that constitute an improvement in accordance with the present invention as described hereinafter.
With reference to the positive temperature coefficient thermistor device shown in FIG. 5, the interior of an insulating case 4, made of resin or the like, is closed by a top 6. Housed within the case is a pair of positive temperature coefficient thermistors 1. Normally the shape of the insulating case 4 is that of a square box, and each of the thermistors 1 is in the form of a disk of a requisite thickness with a terminal/electrode on the faces of the disk.
In the insulating case 4, a common electrode 2 is arranged between the two thermistors 1 to form a configuration whereby the opposed disk faces and terminal/electrode surfaces of the thermistors 1 are each provided with a common electrical connection. The inner surfaces of one pair of opposed side walls 5 of the insulating case 4 are each provided with an electrode 3 having a resilient contact means 7 in pressure contact with the corresponding terminal/electrode surface of the thermistors 1.
In the arrangement shown in FIG. 5, the resilient contact means 7 are electrically conductive springy strips. The resilient contact means 7 are arranged thus to ensure that there is an electrical connection between the electrodes 3 and the terminal/electrode surfaces of the thermistors 1, and to stably maintain the thermistors 1 in their requisite face-to-face position. As such, in some cases the number of these resilient contact means 7 in increased to enhance their function by increasing the number of contact points. An example of this is shown in FIG. 2, in which the resilient contact means 7 are each formed as a pair of parallel strips.
The bottom wall 8 of the insulating case 4 is provided with slits 9 and 10 (FIG. 2) through which the tips 2' and 3' of the common electrode 2 and electrodes 3 project from the case. The dimensions of the tips 2' and 3' of the electrodes projecting from the case are reduced to enable them to be directly connected to a printed circuit board (not shown). Resilient tongues 11 and 12 are punch-formed in the narrow sections of the electrodes 2 and 3 in such a way that they allow the electrodes to be pushed into the slits but by then springing up once they clear the slits prevent the electrodes from being inadvertently pulled back into the case.
A conventional dual-type positive temperature coefficient thermistor device has the above-described structure. The object of the present invention resides in the means used to maintain the mutual alignment of the thermistors 1 in the insulating case 4. In the prior art, as described above, the resilient force of a pair of resilient contact means 7 pressing the thermistors 1 towards each other is used for the purpose. However, a single pair of resilient contact means 7 is not always enough to maintain the position of the thermistors 1 under the various conditions encountered from fabrication and assembly of the device through to actual use.
Even with the force of the resilient contact means 7 urging the thermistors 1 against the common electrode 2, as such force is only exerted on an area at the center of the face of the thermistors 1, strong vibration, shocks and the like can jolt the thermistors 1 out of the vertical, as illustrated in FIG. 6, or can cause them to shift sideways out of mutual alignment, along the common electrode 2 (that is, in a direction normal to the FIG. 6 sheet).
Especially in the case of an application such as that of a degaussing circuit described above in which one of the positive temperature coefficient thermistors 1 is used as a heat emitter and the other thermistor 1 as a heat receiver, that is, a thermocouple application, in addition to causing a major deviation from design and target values of the thermistor device itself, such misalignment of the thermistors also gives rise to major deviation from the expected electrical characteristics of the overall circuit system in which the device is used.
Thermistors can slip out of the vertical while being inserted into the case during the assembly of the device (FIG. 6). Care is needed to avoid this happening, which slows down the assembly process. In practice, thermistors are more likely to shift out of the vertical than to move sideways, and vertical misalignment gives rise to greater variation in the thermal and electrical characteristics.